This invention is directed to a composite granular material tailored to release, upon application to soil, plants or the like, a pesticide in a controlled manner. More particularly, the invention is directed to a particulate material comprising a xe2x80x9ccorexe2x80x9d such as ammonium sulfate which is coated under controlled conditions with a select polymeric membrane and a pesticide such as acephate. A controlled-release polymer membrane is applied as an outer membrane. The material is stable when stored, but will release pesticide at a controlled rate when applied to a plant or the like material in a field environment.
In recent years, because of ecological concerns as well as the need for controlled release of fertilizers, pesticides and the like materials for economical reasons, there has been a concerted effort to coat fertilizers as well as pesticidal materials with polymer coatings which will permit a controlled release of the material upon application to plants or the like in a field environment.
For example, U.S. Pat. No. 6,060,076 discloses methods and devices for providing long-term protection from intrusion by insects and other cold-blooded animals involving a polymeric matrix and a pesticide contained therein.
Further, U.S. Pat. No. 5,939,376 discloses a controlled-release coated agricultural product including agricultural chemicals, seed, or mixtures thereof with a coating of an environmentally degradable amorphous copolymer. A process of making such products involves making the product with a molten copolymer and then cooling to harden the coating of copolymer upon the agricultural product.
U.S. Pat. No. 4,056,610 discloses a microcapsule insecticide composition including microcapsules, each having a polyurea shell with a photostable ultraviolet light-absorbing compound as an integral part of the shell and a liquid fill capable of slowly permeating the shell of a pyrethroid and a biologically synergist thereof. When the polymer is applied as an insecticide, the pyrethroid releases slowly depending upon the thickness and porosity of the capsule wall.
U.S. Pat. No. 4,223,070 discloses filled porous granules sealed with a porous polyurethane membrane entrapping therein a liquid material. The material is allowed to diffuse from the granules at a controlled rate. The porous granules which are partially miscible with water have applied thereto an organic solution comprising the material to be entrapped, an organic polyisocyanate, and a catalytic amount of a catalyst for catalyzing the polymeric reaction.
U.S. Pat. No. 6,080,221 discloses a method of coating fertilizer particles exhibiting porous surfaces under vacuum to form controlled-release particulate fertilizers by drawing a vacuum on the fertilizer particles and applying thereto a water-insoluble resin at atmospheric pressure and, then hardening the fluid resin to form a solid resin. Pesticides may be coated using the disclosed method.
While these described products are recognized to provide certain improvements with respect to the release of insecticides and the like, the formulations in most respects are difficult to produce, lack essential properties in a controlled-release product or simply can stand improvement.
In a related field it has also been recognized that a fertilizer product, such as urea, can be applied to a soil environment in order to control the release of the fertilizer over a period of time. This permits a single application of the fertilizer which will last several months and possibly an entire growing season, avoiding the need for further applications. For example, U.S. Pat. Nos. 4,716,659; 4,804,403, and 4,969,947, in the name of William P. Moore and now assigned to the assignee of the present application, disclose an attrition-resistant, controlled-release fertilizer comprising a water-soluble central mass, such as urea, containing nucleophilic reaction functional groups surrounding and chemically bonded to a base coating formed by reacting a molecular excess of a coupling agent, such as a polyisocyanate, with the nucleophilic groups of the central mass and a water-insoluble layer surrounding and chemically bonded with the base coating formed by the reaction and polymerization of the excess functional groups of the coupling agent. These products provide outstanding controlled-release fertilizer products.
The present invention is directed to further improved pesticidal materials having controlled-release characteristics when compared with the known materials described in the known prior art.
In accordance with the present invention, pesticidal products are manufactured having excellent controlled release of the pesticide by bonding the pesticide or a pesticide mixture to a xe2x80x9ccorexe2x80x9d material such as ammonium sulfate using reactive polymer-forming components. Specifically, a core granule has applied thereto an inner polymer membrane. A pesticide or pesticide mixture is applied to the polymer membrane on the core material and bonded thereto, preferably using the reactive components of a polymer matrix. An outer controlled-release polymeric membrane is applied to the inner polymer matrix. The outer controlled-release membrane is formed by using reactive components, such as a polyisocyanate and a polyol such as a polyester. The components of the membrane are controlled so as to permit controlled release of the pesticide and possibly the core granular material when applied to the soil where the product is in contact with moisture.
For convenience, the present invention will be described with reference to an insecticide as the pesticide, and specifically acephate; ammonium sulfate as the granular core material, and a polyurethane as both the inner membrane and the outer controlled-release membrane. It is to be understood, however, that other granular materials such as urea, potassium chloride, clay and the like can be utilized as the core material. Ammonium sulfate is, however, a highly preferred material and provides an excellent pesticidal composition. Further, in addition to using acephate as the pesticide, other pesticides can be utilized, including other insecticides, as well as other components including herbicides, fungicides, plant growth regulators, and the like. The selection of acephate as the pesticide and ammonium sulfate as the granular core material is due to the excellent product formed with these materials and for convenience of description.
The present invention will be described with respect to a controlled-release pesticidal material comprising ammonium sulfate as the xe2x80x9ccorexe2x80x9d material, an inner polymer membrane surrounding the core granular material, acephate as the pesticide, and a polyurethane membrane as a controlled-release membrane. In Examples 1 and 2 which follow, these materials are utilized. It is to be understood, however, that modifications can be made in addition to components used with respect to the number of coatings applied to the core material and to the amount of a active component utilized.